Adjustable Output Regulator Circuit Diagram using 7805 IC

You might use 78xx series voltage regulators when circuit an adjustable output regulator. And the following circuit diagram shows the adjustable output regulator using one of 78xx series from Motorola, MC7805.

The minimum voltage can be obtained from this circuit is 2.0V greater than the regulator voltage. An addition of an op amp may take adjusment to higher or intermediate values while retaining regulation characteristics.